entity-relationship

问题 my question is a two part issue. I am using the repository and unit of work pattern with entity framework. I have the following StockTransferRepository and StockTransfer is my aggregateRoot. Public Class StockTransferRepository Inherits WMSBaseRepository(Of StockTransfer, Int64, Dictionary(Of String, String)) Implements IStockTransferRepository Public Sub New(uow As IUnitOfWork) MyBase.New(uow) End Sub Public Overrides Function GetObjectSet() As IQueryable(Of StockTransfer) Return

问题 how are the two different? Since both of the relationships consist of one set of objects say A which cannot exist independently and another set of objects say B whose existence is necessary for the existence of objects in the set A. So are the two same or are their some fundamental differences that I am missing out on? 回答1: "Composition relationship" isn't a formal relationship type in ER. If I take it to mean a binary relationship (a,b) which is left-total (every a is related to some b) and

问题 I'm not quite sure how to approach this problem: Price for one-way trips is different than price for round trip itineraries. In the backend, I have a table for storing the itinerary (which yields an id). I have another pricing table, which defines what is the price of this id from startDate to endDate. My itinerary table can only represent information for one way travel. How do I model round trip itineraries ? One way to deal with this was: have another column in the table: returnId if

问题 I am trying to build my app on android studio virtual simulator, I have successfully tested on api level 21 and above now I am testing lower level api 19, but whenever I run i will get this error: Error:Execution failed for task ':app:transformClassesWithJarMergingForDebug'. com.android.build.api.transform.TransformException: java.util.zip.ZipException: duplicate entry: com/android/volley/Request$Priority.class This is my gradle file: apply plugin: 'com.android.application' android {

问题 I did a bit of searching but can't find a same problem / question. I have a question regarding the table naming (in the database) when EF creates a table encountering InverseProperty DataAnnotation "Dummy/Demo code" : public class User { public Guid Id { get; set; } public String Name { get; set; } public virtual List<Event> InvitedEvents { get; set;} public virtual List<Event> AcceptedEvents { get; set;} public virtual List<Event> DeclinedEvents { get; set;} } public class Event { public

问题 I am new to Objectify and trying to implement One-to-Many relationship. I have entities Organization and entity Person . Organization has @Transient property List< Person > contactPeople . Class Person has @Parent property Key< Organization > organizationKey which I can set via setter. I'd like to persist contactPeople in @PrePersist handler of Organization. In order to do that I need to set parent key in Person. Wiki here says: "You can't update @Id or @Parent fields in a @PrePersist

问题 I have a database in which there is Country, city , states , postcodes in one table with huge set of records. I want to normalize the database structure to avoid redundancy and remove any data duplication. Should I split database and make separate tables for Country, City, state and postcode? Or merge country , city , state, postcode in Address table? 回答1: The following tables could be used for addresses in North America. Counties (which would also contain Parishes and other similar

问题 I've read that you need to keep entities that have a relationship in sync, i.e. when you remove a child from a parent you should also set the attribute that holds the parent to null in the child entity. In my example I have the following parent entity: public class Parent { @OneToMany(mappedBy = "parent", cascade = CascadeType.ALL, orphanRemoval = true) private List<Child> children; } And the child: public class Child { @ManyToOne(optional = false) private Parent parent; public void setParent

问题 I have the following issue: I have this entity, let's call it ENTITY_THREE , which is part of a arc barred relationship : Three entities ENTITY_ONE , ENTITY_TWO and ENTITY_THREE which are part of an arc barred relationship Please note that ENTITY_THREE has a composite primary key: ID , ID_OF_ONE , ID_OF_TWO and ENTITY_TWO has a composite primary key as well: ID , ID_OF_ONE . Now, according to the description of the assignment, if ENTITY_TWO has more than 1 of ENTITY_THREE , ENTITY_THREE needs

问题 How can i define relationship between subclasses in XML, for example a class researcher has two subclass Paper and author . 回答1: Normally you would be using an XML schema to describe relationships in an XML file. But I seriously doubt you should make a model where researcher has subclass paper and author, it seems more like researcher is related to the class Paper in the role of Author. All of this you can describe in XML Schema. 来源： https://stackoverflow.com/questions/432699/how-to-reflect